This invention relates to rotary driven members and more particularly to torsionally elastic power transmission assemblies capable of absorbing or isolating torsional shocks and vibrations in a power drive train.
Power transmitting devices are known which are capable of dampening or isolating torsional shock loading and minimizing noise and vibration by the use of resilient cushioning means. Rubber cushions, for instance, are adapted to yieldingly transmit rotary motion between mating lugs of an integral hub and rim assembly. Typical known applications include cushioned sprockets for use with roller chain or synchronous belting (timing belts), direct gear drives, and torque transmission between shafts (flexible couplings), for instance. Various industrial applications are contemplated including those set forth in Koppers Company "Holset Resilient Couplings" catalog, March, 1973. Additional relevant prior art include, for instance, Croset U.S. Pat. No. 2,873,590, Kerestury U.S. Pat. No. 3,314,512 and the above-referenced copending applications.
The rubber cushions used in the torsionally elastic couplings of the referenced copending applications were especially effective in smoothing out vibrations and modulating torque peaks for the primary drive of motorcycles using synchronous drive belts. However, it was found that when subjected to abusive driving techniques, such as "speed shifts" where gear shifts are made without letting off on the throttle, the driven spocket experienced very high torque peaks. During the speed shift the torsionally elastic driver sprocket assembly would wind up (along the "soft" portion of the torque deflection curve) allowing the driven sprocket to slow down. Subsequently when the flattened or "stiff" portion of the torque deflection curve was reached as the cushions filled their associated cavities, a large torque was suddenly applied causing a very high peak load on the drive due to inertial effects. In some cases the belt failed by tooth shear or breaking of the tensile reinforcement.
It is a primary object of this aspect of the invention to overcome the problems associated with such abusive conditions and to provide an elastomeric cushion spring having desirable spring rate and damping properties allowing much higher torques to be transmitted while still operating on the initial sloped ("soft") portion of the torque deflection curve, and simultaneously accommodating relatively large angular deflections for the drive.
In another vehicular application there is a trend toward extensive use of dynamically unbalanced four and six cylinder diesel and other engines exhibiting severe speed excursions at low rpm, especially for automobiles and trucks which are particularly vibration prone. Accessory drives for these engines transmit power from the crankshaft sheave to various driven sheaves usually linked with a number of separate V-belts or V-ribbed belts, or in the case of the so-called serpentine drive with a single V-ribbed belt, all working on a friction drive principle. These rough running engines, particularly the four and six cylinder diesels, have such high rpm excursions at idle speeds (below about 1000 rpm) that V-ribbed belts and other friction drive belts undergo tremendous slippage and elastomeric material shear relative to the tensile section, causing the belt and sheaves to heat up to such temperatures that in severe cases the belts have failed after only a single hour of operation on the drive.
In this latter aspect it is a primary object of this invention to overcome the slippage and heat build-up problems aforementioned associated with V-belt or V-ribbed or similar type friction drives. Examples of serpentine drives and other belt configurations useful in this aspect of the invention, and which drives and configurations are hereby incorporated by reference, include those disclosed in Fisher et al. U.S. Pat. No. 3,951,006.